HS6 cold-starting procedure

[Clifford Pope]

I'm pretty confident I've got these set up and tuned correctly. The engine runs beautifully and smoothly, with the expected bags of power. When hot or even just mildly warm it restarts instantly without any accelerator necessary. It just starts and immediately idles.

I know after a period of non-use the pump needs priming. I don't think fuel can run back to the tank out of the float chambers past the needle valves - there's an air gap on top of the petrol level in the chambers. There are no drips - the bottom of bowls are always absolutely dry. So it seems the petrol simply evaporates - they are vented to a hot engine after all.

That's fine - I just accept it needs priming, about half a dozen strokes as I hear petrol sloshing into the obviously empty chambers.
But why, despite priming the petrol, does it still need from 5-10 seconds of cranking to start from cold? Can it really take that long just to draw mixture past the jets and into the intake?
I've found from experiment that the fastest way of starting when cold is full choke and no accelerator. When it does fire it immediately runs well, I release the choke, and it will idle smoothly or pull away strongly. No black smoke, no needing to rev it to clear excess fuel.

Is this normal? Is there a recommended starting procedure?

There seems to be a good spark. Gaps set at 28 thou, timing 8 degrees BTDC, new coil, cap, points, rotor, HT leads, but it's always been like this, even before replacing anything.

[johnnydog]

Not sure why your plugs at 28 thou as you haven't got electronic ignition fitted? 25 thou is the normal plug gap.
After long periods of inactivity, I always have fuel in the glass bowl of the fuel pump - with Strombergs and HS6's.
If I was to start any of the Triumphs straight from cold with sufficient choke, they would start after a couple of seconds, but I don't like to do that - from cold, I always turn the engine over on the starter for about 5 -10 seconds without any choke to attain some oil pressure. I then pull the choke out whilst continuing to turn the engine over at which point it immediately fires and the oil light extinguishes immediately. This is even after a period of weeks without being run.
I have never felt or had the need to prime the pump after a period of not being run. Rather than instantaneous starting from cold (it doesn't matter when hot), I would rather turn the engine over to get the fuel through and at the same time getting some oil pressure before the engine fires. So having to churn the starter before the engine fires wouldn't particularly bother me.
Incidentally, I don't have the oil filter adapter set up on any of my cars.
The only time I have had fuel loss out of the carbs was on Strombergs but it was a leak with physical evidence of the fuel leaking past the needle / flat valves due to poor quality modern replacements. The fuel leaked into the air filter box and was dripping of the bottom of the mixture screw. Not the same issue as you have Clifford - so not much help to you really!

[Alec]

Hello Cliff,

the Reliant Scimitar I once owned had the same problem, and many owners fitted an electric fuel pump to overcome this problem.

Alec

[Clifford Pope]

Thanks - some interesting points there.
I don't know why I've always had 28 thou stuck in my mind - on checking you are right, the plugs are meant to be 25 (25.6 actually, converting .65 mm). I don't suppose it is that critical, but worth putting right.
There's always petrol in the glass bowl - it's lower than the fuel tank. But I don't think petrol can syphon out of the float chambers, because there's vented air above the petrol.

I can understand the merit of cranking to build up oil pressure, which would of course prime the fuel too. I've got a filter conversion fitted, so the oil doesn't run back, hence my priming the fuel pump lever.

It appears from both your posts that for some reason priming the pump lever does not fill the carburettors as effectively as cranking the engine. It's hard to see why that should be - it's surely the same action - moving the diaphram up and down and pumping petrol into the float chambers until the needle valves shut the flow off. Nor can I see why an electric pump would be any more effective, unless it has a higher pressure forcing more petrol through the valves so raising the level in the chambers.
Does that mean the approved setting for the level is wrong, and it ought to be a bit higher?

At any rate, it appears to be normal to have to crank for an appreciable time with these carburettors. I'm used to all other cars I have ever owned firing instantly on cold starts (after appropriate priming). Certainly my previous 2000 with Strombergs did.

I'll try the idea of cranking for a few seconds before pulling the choke out. I'd never heard of that technique - I've always set the choke before starting.

[Alec]

Hello Cliff,

as a point of accuracy, the metric setting is a conversion from the original 25 thou.

The idea of an electric pump is that it is easier, merely switch on the ignition. There is a problem with cranking the fuel pump lever because it depends on where the engine stops, if it's on the wrong part of the cam the fuel pump will not pump with the priming lever or do so ineffectively.
How long is the car standing as it should take weeks (at a guess) for the fuel chambers to evaportae to near empty? Unless it is something to do with the heat of the engine when you stop, I really don't know?

Alec

[Clifford Pope]

It appears to be a known problem. On the TR6 forum I've just found a link to an after-market Moss heatshield in the form of a trough, which bolts between the carbs and manifold, and shields the underside of the carburettors from the exhaust manifold.

https://www.ebay.co.uk/itm/172266268005

That seems to be what it needs. No problem when on the move because of airflow, but after stopping the carburettors will be sitting in the rising current of hot air.

[johnnydog]

HS6's on the facelift 2500 models were fitted with an individual carburettor heat shield on each carb as standard, but they were prone to breaking by the edge of the their mounting if caught whilst accessing components nearby. They were made of a heat resistant fibre board material about 1/16" thick and were flat mounted between the inlet manifold and carburettor on the 4 stud flange and were quite vulnerable. They didn't protect the underside of the carb from heat. I think stainless replacement are now available.
Strombergs, in my experience, are more prone to fuel evaporation from engine heat than SU's, although originally heat shields were never fitted. There are heat shields available now for six cylinder Triumphs with Strombergs, which are supposedly supposed to reduce the fuel evaporation.
I wouldn't have thought an electric fuel pump would force more fuel through into the float chambers, as the needle valve ought to shut the fuel supply off when the desired level of fuel is available, otherwise they would be effectively flooding on a regular basis. Flooding does seem to be an quality issue associated with the 'new' needle / float valves on Strombergs rather than with HS6's in my experience.

[wild bill]

I'm with John on the starting issue.I ALWAYS crank the engine for 10 seconds, then full choke.I can predict to milliseconds when the car will start, and usually give a flick of the finger when I suspect it will fire--and I am seldom wrong! Also never rev it until the gauge is up to 95-100 PSI, then only after slipping the choke back to a just over tick over level.
Also,I NEVER press the clutch before and for around 30-40 seconds after start up,so as to minimise any wear to the thrusts, seems to work for me...
I have never thought of the cranking over as a problem, more a ceremony of starting procedure, that I am more than content to fulfil.
Just my thoughts,
Bill.

[Clifford Pope]

Well, that seems a pretty strong support for cranking - I'll just try to live with it!
It's hard after a lifetime of cars that all started on the button to have one where everyone tells me 10 seconds of cranking is normal.

I'm just intrigued to know why hand priming isn't as effective at raising petrol as cranking - it seems to suggest that vacuum from the intake side plays more of a role with this particular carburettor.

[Alec]

Hello Cliff,

for what it's worth, and it's a long time since I had a carburettor Triumph, I don't remember any cold starting problems requiring long cranking, but my car was used near enough daily.

Regarding the oil pressure from start, Triumph designed the oil pump to stay full of oil when the engine stops by the simple design feature of the oil inlet being on on top of the pump. (The oil suction passes up a duct on the side of the pump) Ensuring the oil level is kept high will reduce the very short time it takes for the pump to refill the suction pipe and filter, if using the original one.

Alec